Objective To isolate and identify the pathogen responsible for causing hemorrhage in Mugilogobius chulae, and to investigate its route of transmission, providing a technical basis for microbial quality control in M. chulae. Methods The pathogen was isolated from the liver of diseased M. chulae. The morphological, biochemical, and molecular characteristics were used to identify the isolated bacteria. An artificial infection experiment was carried out to assess the pathogenicity of isolated strains. Double PCR of Aeromonas hydrophila virulence genes was used to screen samples of M. chulae, Brachionus plicatilis, Artemia nauplii, and water. Results The dominant strain PYMc15 - 1 was isolated from diseased M. chulae. The characteristics (API ID32E) of PYMc15-1 corresponded to A. hydrophila. The gyrase subunit B (gryB) gene sequence of the strain possessed high similarity with those of A. hydrophila registered in GenBank. Phylogenetic tree analysis of Aeromonas based on the gryB gene showed that strain PYMc15-1 clustered together with A. hydrophila. The hemolysin ( hlyA) and gas lysin ( aerA) genes could be amplified from the strain PYMc15- 1, and the median lethal dose (LD₅₀ ) of PYMc15-1 to healthy M. chulae was 1. 2 × 10⁴ cfu / fish. Wild M. chulae, Artemia nauplii, and wild B. plicatilis were positive for pathogenic A. hydrophila, while the closed colony of M. chulae, indoor cultured B. plicatilis, and seawater samples were negative for pathogenic A. hydrophila. Conclusions A. hydrophila can naturally infect M. chulae. For wild M. chulae, living feeds are potential vectors of A. hydrophila. A. hydrophila should be tested when introducing M. chula and living feeds.